1. Technical Field
The present invention relates to a printing device, a printhead, and a method of positioning a print medium in the printing device.
2. Related Art
Printers that detect an indexing mark such as a notch or a position recognition marker disposed to the print medium and position the print medium based on the detected mark are known from the literature. See, for example, JP-A-2013-22861. The device taught in JP-A-2013-22861 detects the perforation or a slit formed between each page of a continuous medium such as fanfold paper or roll paper by an optical sensor disposed to the media conveyance path. After detection by the optical sensor, an operation for setting the position to cut a label after printing to the detected perforation, for example, is executed referenced to the detected position. Printers of this type can typically convey the print medium in both forward and reverse directions, but when the conveyance direction is changed to the opposite direction, the position can shift or slip due to backlash. To solve this problem, JP-A-2004-276396 teaches measuring and compensating for this backlash.
Printers that have a platen roller disposed opposite a printhead, and print while conveying the print medium held between the printhead and platen roller, are also common. This type of printer enters a standby mode while the print medium is held between the printhead and platen roller, and a long time can pass with the print medium held pressed against the printhead. As a result, when printing to a print medium with a coated printing surface that can easily stick when pressed and held against the printhead, and the printer is left in the standby mode for an extended time, the print medium may stick to the printhead. To solve this problem, JP-A-2012-61849 teaches removing print media that has stuck to the printhead by moving the printhead in a direction that changes the position in contact with the platen roller while the printhead is pressed against the platen roller.
Variation in the conveyance distance can also occur during print media conveyance for reasons other than backlash. For example, slipping can occur when conveying media in a specific conveyance direction due to the construction of the conveyance mechanism that conveys the print media. When the print medium is conveyed in a specific conveyance direction, this type of slippage is the difference between the conveyance amount of the operation conveying the print medium, and the actual amount that the print medium was conveyed (moved). If the actual conveyance amount differs according to the conveyance direction, this difference can result in a difference, between the intended conveyance amount and the actual conveyance amount. As a result, the actual position of the print medium may deviate from, the expected position even if control that sets the position of the print medium to a specific indexed position is applied. Because this deviation is not necessarily the same every time the conveyance direction changes and backlash occurs, accurate measurement is difficult.
The cumulative effect, of differences in the conveyance amount in each conveyance direction could conceivably be eliminated by conveying the print medium in only one direction for positioning without changing the conveyance direction. Because the print medium cannot be reversed in this configuration, the print medium may be conveyed a greater distance to reach the desired indexing position, and waste increases.
The printhead disclosed in JP-A-2012-61848 has a support frame to which the head unit is affixed, and the position of this support frame when the support frame moves is limited by stops formed on the inside surfaces of the side panels of the case. If there is variation in parts of the printhead, such as positioning error or twisting of the head unit, movement of the printhead may be limited by the stops and pressure may be uneven when the printhead is pushed to the platen roller, print quality may therefore drop, and media conveyance may be skewed.